TBH I don't even understand why Android Auto needs to exist in the first place.
The same (or even better) functionality can be achieved by using a standard video output (DisplayPort, HDMI) from the device to the in-car screen, while the touches on the in-car screen can be translated into USB mouse position and clicks on the device (unless there is a better touch protocol).
I know there are regulations about live video on in-car screens, but 1. That does not stop people from watching videos on their phones while driving and 2. Somehow that does not apply to maps?
This, unfortunately, has been a thing for over a decade. I was excited to discover that Samsung Galaxy S3 (i9300) is/was one of the better-supported phones for custom ROMs... until I realized that the one I have is a Sprint / Virgin Mobile version (d2spr), which looks the same but uses a different SoC entirely.